The present invention relates generally to a new and improved nozzle throat area control apparatus and method and, more particularly, to such an apparatus and method for controlling both thrust level and thrust vector angle in a rocket motor or other similar propulsion device.
U.S. Pat. No. 2,968,919 to Hughes et al. discloses a variable area nozzle having a plurality of circumferentially spaced vanes in the nozzle throat, with means being provided to position the vanes within the throat and restrict fluid flow therethrough in response to changes in pressure upstream from the throat. In operation, pressure within the combustion chamber is delivered to a chamber on one side of a piston connected to each vane. When the combustion pressure exceeds the force of a compression spring on the other side of the piston, the vanes are moved radially outwardly to reduce their restriction of fluid flow through the throat of the nozzle. As the combustion pressure is reduced, the springs will move the vanes inwardly to restrict fluid flow through the nozzle throat. The nozzle construction of Hughes et al. is subject to certain disadvantages. First, the actuation system for the vanes must be constructed to handle the hot combustion gases that are conveyed to the piston for each vane. Second, the vanes are of a size, positioning and construction such that they are not capable of moving far enough into the nozzle throat area to close it or severely restrict it. Third, the vanes are not independently movable and cannot be selectively controlled for specific operations.
The patent to Mancus, U.S. Pat. No. 3,743,184, discloses a variable area nozzle construction utilizing four blades that can be radially moved into and out of the nozzle throat area. Each of the blades is also rotatable to provide thrust vector control. The nozzle construction of Mancus is subject to certain disadvantages. First, it is necessary to move the blades both radially and to rotate them to obtain both throat area and vector control. This results in a more complicated construction for effecting movement of each blade. Second, the blades are substantially smaller than the size of the nozzle throat area and thus are not capable of severely restricting or substantially closing flow through the nozzle throat area in cases where this may be necessary or desirable.
The new and improved nozzle throat area control apparatus and method are not subject to any of the above-described disadvantages of the devices in the Hughes et al. and Mancus patents, or of other nozzle throat area control systems previously or currently used or in the prior art. Additionally, the nozzle throat area control apparatus and method of the present invention possess many advantages that are not found in the prior art.
The nozzle throat area control apparatus of the present invention comprises a pair of plungers that are slidably mounted in the nozzle housing adjacent the throat thereof. The plungers may be in opposed or other suitable relation, and are of a size that is substantially equal to the size of the nozzle throat so that the plungers may be moved into the nozzle throat to severely restrict the flow of combustion gases therethrough or to substantially close the throat.
The plungers are independently movable by any suitable means, such as gas generating devices, mechanical, electro-mechanical, hydraulic or pneumatic actuating devices. The independent movement of the plungers can be used to effect thrust vector control as well as thrust level or combustion chamber pressure control.
In one embodiment, a dual level apparatus is provided in which gas generating devices are used to move the plungers from outer positions to inner positions to restrict flow through the nozzle throat after a predetermined period of operation. In a second embodiment, actuators are used for variable control of the positions of the plungers depending on the combustion chamber pressure desired or the thrust vector control desired. In a third embodiment, means are provided for reigniting the propellant after a predetermined period after which burning has been terminated, and actuating means are provided for the plungers to move them to desired positions to control burning of the propellant and thrust vector control during the initial period of burning and the re-ignition period.
The new and improved nozzle throat area control apparatus and method of the present invention is simple in construction, reliable in operation and operable to provide more uniform thrust, when desired, by effectively controlling the propellant combustion chamber pressure by selectively restricting flow through the nozzle throat area. By independent movement of the plungers, thrust vector control can also be easily effected.